I dont know if this is the case with the 4.0's but with the new 5.0's that are in the mustangs and F-150's the mustangs have about 30 more HP than the F-150's but the F-150's peak torque and HP come in at a lower RPM than the Mustang's to be better suited for truck use. (towing ect) I bet if you could compare HP and TQ curves between mustang 4.0 and the ranger 4.0 you would see the same thing.